In physics class, the girl to boy ratio is $8$ to $10$. If there are $30$ boys, how many girls are there?
A ratio of $8$ girls to $10$ boys means that there is a group of $8$ girls for every group of $10$ boys. If there are $30$ boys, then there are $3$ groups of $10$ boys each. Because we know the ratio is $8:10$ , there must be $3$ groups of $8$ girls each. There is a total of $24$ girls in physics class.